1. Field of the Invention
The present invention relates to a liquid crystal display device used for displays of office automation apparatuses, audio and video apparatuses, and the like, and a method for fabricating such a liquid crystal display device.
2. Description of the Related Art
A conventional transistor-type active matrix driven liquid crystal display device will be described with reference to FIGS. 6A and 6B, as the first prior art example. FIG. 6A is a perspective view of the conventional liquid crystal display device, and FIG. 6B is a sectional view taken along line 6Bxe2x80x946B of FIG. 6A.
Referring to FIG. 6B, the conventional liquid crystal display device includes a first substrate 601 (hereinbelow, referred to as a counter substrate) and a second substrate 602 (hereinbelow, referred to as an active matrix substrate) disposed to face each other with a predetermined gap therebetween. A liquid crystal layer 612 is provided between the substrate 601 and 602. Referring to FIG. 6A, the active matrix substrate 602 includes: a plurality of parallel source bus lines 609 and a plurality of parallel gate bus lines 610 which are formed on the surface of a glass substrate 620 facing the liquid crystal layer 612; and thin film transistors (TFTs) 611 disposed at the respective crossings of the source bus lines 609 and the gate bus line 610. Pixel electrodes 608 are formed on the surface of the glass substrate 620 facing the liquid crystal layer 612 and connected to drain electrodes of the corresponding TFTs 611. A voltage is applied to each of the pixel electrodes 608 for controlling the orientation direction of liquid crystal molecules in the liquid crystal layer 612.
Referring to FIG. 6B, the counter substrate 601 includes: a plurality of colored portions 605 on the surface thereof facing the liquid crystal layer 612 at positions corresponding the pixel electrodes 608 of the active matrix substrate 602; and a counter electrode 603 formed covering the colored portions 605. A black matrix (BM) layer 604 made of a light-blocking material is disposed to fill gaps between the adjacent colored portions 605.
Hereinbelow, a color filter layer as used herein will be described. For example, when pixels are arranged in a stripe shape, stripe-shaped colored portions of red (R), green (G), and blue (B) are arranged cyclically in parallel. A color layer is composed of a plurality of stripe-shaped colored portions of a single color corresponding to respective pixel electrodes. Such color layers constitute a color filter layer. The color filter layer as used herein does not include the BM layer formed between the adjacent colored portions. Herein, a region of the liquid crystal display device defined by each of the pixel electrodes is called a pixel region.
Referring back to FIGS. 6A and 6B, in the conventional liquid crystal display device, a scanning signal voltage is sequentially applied to the gate bus lines 610 so as to switch on the TFTs 611 connected to the respective gate bus lines 601, thereby allowing a specific display signal voltage to be written in each of the pixel electrodes 608 and held for a certain time period. The liquid crystal layer 612 interposed between the substrate 601 and 602 is driven with the potential difference between the voltage at each of the pixel electrodes 608 and a counter voltage applied to the counter electrode 603.
Two exemplary methods normally used for fabricating the counter substrate having a plurality of colored portions as described above will be described with reference to FIGS. 7A to 7E and 8A to 8E. FIGS. 7A and 8A are flow charts showing normal fabrication steps for the counter substrate having colored portions. FIGS. 7B to 7D and 8B to 8D are plan views, together with corresponding sectional views, at the respective fabrication steps. FIGS. 7E and 8E are sectional views of the respective complete counter substrates.
Herein, a normal dry film fabrication method will be described with reference to FIGS. 7A and 7E. A resin film (dry film) having red (R) pigments dispersed therein is laminated to a glass substrate 720, followed by steps such as exposure to light, development, and baking, to form an R color layer composed of a plurality of stripe-shaped R colored portions 705.
A dry film having (G) pigments dispersed therein is then laminated to substantially the entire top surface of the substrate covering the R colored portions 705. This is followed by steps such as exposure to light, development, and baking, to form a G color layer composed of a plurality of stripe-shaped G colored portions 706.
A B color layer composed of a plurality of stripe-shaped B colored portions 707 is then formed by repeating the process for the R colored portions 705 and the G colored portions 706 described above. Thus, a color filter layer composed of the R, G, and B three-color layer is completed. The colored portions are formed so as to correspond to respective rows of pixel electrodes.
Referring to FIG. 7E, after the formation of the color filter layer, a dry film having carbon particles dispersed therein is laminated to the resultant substrate. Using the color filter layer composed of the colored portions as a mask, the back surface of the substrate is exposed to light, followed by development and baking, to form a BM layer 704 for light-blocking the regions where the colored portions of the color filter layer are not formed. ITO is then deposited over the entire top surface of the resultant substrate to form a counter electrode 703. Thus, a counter substrate 701 is fabricated. As the BM layer, a metal film may also be used as shown in FIG. 8B as a metal BM film 804.
FIGS. 8A to 8E illustrate a fabrication process of the counter substrate by a spin coat method. Resin materials having color pigments dispersed therein are applied to substantially the entire top surface of a glass substrate 820 by spin coating, to form R, G, and B colored portions 805, 806, and 807, so as to fabricate a counter substrate 801.
Hereinbelow, a common transfer portion formed in a conventional liquid crystal display device such as described above will be described with reference to FIGS. 9A to 9C. The common transfer portion as used herein refers to a portion for securing an electrical connection between the counter substrate and the active matrix substrate to be used as a terminal formed on the active matrix substrate for applying a voltage to the counter electrode.
FIG. 9A is a plan view, together with a corresponding sectional view, of a conventional liquid crystal display device. FIG. 9B is a plan view, together with a corresponding sectional view, illustrating a common transfer portion of an active matrix substrate 902 of the conventional liquid crystal display device. In FIG. 9B, the reference numerals 909 and 910 denote source bus lines and gate bus lines, respectively. FIG. 9C is a plan view, together with a corresponding sectional view, illustrating a common transfer portion of a counter substrate 901 of the conventional liquid crystal display device. In FIG. 9C, the reference numeral 905 denotes colored portions.
Referring to FIG 9B, the active matrix substrate 902 includes a common transfer electrode 917 formed between adjacent source driver connection blocks in a source terminal extension portion. The common transfer electrode 917 is connected to a common line at a position on the periphery of the display panel, and is electrically connected with a counter electrode 903 (FIG. 9C) of the counter substrate 901 via carbon paste 918. The number of such common transfer electrodes 917 formed for one display panel may be appropriately determined depending on the definition level of the panel, the size of the panel, the difference in resistance from the transparent counter electrode, and the like. For example, for a panel equivalent to Type 10 VGA, about four to eight common transfer electrodes are normally provided.
Referring to FIG. 9C, in the counter substrate 901, ITO is deposited using a mask so that an ITO portion 903 is formed on the area of the counter substrate 901 corresponding to the common transfer electrode 917 of the active matrix substrate 902, so that the ITO portion 903 comes into contact with the carbon paste 918 of the active matrix substrate 902. The resultant connection portion of the counter substrate 901 has a structure of a glass substrate 920/a BM layer 904/the ITO portion 903/the carbon paste 918 formed in this order. Alternatively, ITO may be formed over the entire surface of the counter substrate 901, instead of masking. In this case also, the same structure as described above is obtained.
The counter substrate 901 and the active matrix substrate 902 fabricated as described above are placed to face each other with a predetermined gap therebetween. While a sealer 919 is provided between the substrate 901 and 902 along the periphery thereof, a liquid crystal material is injected into the gap between the substrates 901 and 902 so as to be sealed to form a liquid crystal layer 912. The liquid crystal display device is thus fabricated. When a twisted nematic (TN) liquid crystal material is used for the liquid crystal layer, the gap between the substrates 901 and 902 is normally set at about 4 to 5 xcexcm. Such a gap is realized by dispersing dielectric beads having a diameter of about 4.5 to 7 xcexcm over the entire surface of either the counter substrate 901 or the active matrix substrate 902. Such dielectric beads are dispersed in an unspecific manner over the entire surface of the substrate including the portions above the pixel electrodes as long as no aggregation or the like is generated.
In the first prior art example described above, as shown in FIG. 6B, the source bus line 609 and the counter electrode 603 form a capacitance component therebetween with only the liquid crystal layer 612 existing therebetween. Therefore, if a capacitance coupling is formed between the source bus line 609 charged with a signal and the counter electrode 603, a signal display may be generated on the source bus line 609, generating a difference in write voltage between the signal input terminal and the signal non-input terminal of the source bus line 609. This reduces the display quality of the liquid crystal display device.
Another problem is as follows. Each of the pixel electrodes 608 is influenced by an electric field from not only the portion of the counter electrode 603 located right above the pixel electrode 608, but the entire counter electrode 603. This influence of the electric field from the counter electrode 603 will be described with reference to FIG. 6B. Liquid crystal molecules located near a point B on the pixel electrode 608 are strongly influenced by electric fields from points D, E, F, and the like on the counter electrode 603 closer to the point B. They are also influenced by electric fields including slant components from the points D, E, F, and the like. This may disturb the orientation of the liquid crystal molecules.
As a result of the disturbance of the orientation of the liquid crystal molecules, transmitted light from a backlight incident on the region of the pixel electrode 608 is scattered at points of the periphery of the pixel electrode 608 such as the point B. This reduces the contrast of the liquid crystal display device.
A liquid crystal display device for minimizing the influence of the slant components of the electric field to reduce the display defect is disclosed in Japanese Publication for Opposition No. 2520595. This liquid crystal display device, as the second prior art example, includes a plurality of stripe-shaped counter electrodes in place of the counter electrode described in the first prior art example.
In order to form stripe-shaped counter electrodes, however, a photolithographic step and an etching step are required to pattern the film for the counter electrode. This increases the number of steps, reduces the yield, and thus increases the production cost. Moreover, when the stripe-shaped counter electrodes are formed for a large-size and/or high-precision liquid crystal display device, the interconnection resistance of the counter electrodes increases, reducing the display quality,
As the third prior art example, Japanese Laid-Open Publication No. 5-249494 discloses a liquid crystal display device where steps on a substrate surface formed around bus lines are angularly controlled for reducing the generation of reverse tilt domains and thus improving the display quality. Reverse tilt domains are generated due to a failure in the control of the orientation direction of liquid crystal molecules caused by a failure in the alignment processing during the step of forming an alignment film. Alternatively, a liquid crystal display device having superficial concave grooves formed between adjacent pixel electrode portions is disclosed in Japanese Laid-Open Publication No. 7-20497.
However, in the above-described structures of the active matrix substrate, although the generation of the reverse tilt domains is suppressed, the problem of the influence of slant components of the electric field is not solved. As a result, it is not possible to completely inhibit the generation of the reverse tilt domains.
As the fourth prior art example, Japanese Laid-Open Publication No. 6-82795 and No. 8-32820 disclose the following liquid crystal display device. That is, in order to reduce the amount of beads scattered on the surface of the pixel electrode portions to improve the display quality, a potential difference is provided between bus line regions made of metal and the like and the other regions to allow beads to attach only to specific portions.
However, in order to fabricate a liquid crystal display device with the above structure, respective bus lines must be charged. It takes time to position terminals for charging under substantially an equal pressure. Moreover, for a high-precision liquid crystal display device, a uniform charging is difficult, requiring the provision of a specific structure or step for interconnecting. Fabricating such a liquid crystal display device increases the production cost.
In the liquid crystal display devices of the first to fourth prior art examples described above, the components for driving the pixel electrodes, such as the switching elements, the gate bus lines, and the source bus lines, are disposed on the second substrate. In order to electrically isolate functional films (e.g., conductive films and semiconductor films) for these components from one another, the components are arranged with predetermined spaces from one another on the same plane. In the regions corresponding to such spaces, it is not possible to apply a voltage to the liquid crystal layer to control the light blocking and transmission by the liquid crystal layer. The black matrix (BM) layer therefore needs to be disposed on the first substrate to block light from these regions. In such liquid crystal display devices, the source bus lines are arranged in the regions where the BM layer is formed. Since the metal film constituting the source bus lines also serves as a light-blocking layer, only a small portion of the regions covered with the BM layer is substantially blocked from light by only the BM layer made of a photosensitive resin material.
In the liquid crystal display devices of the first to fourth prior art examples, the gate bus lines and the source bus lines are arranged on the same substrate via an insulating film therebetween. This tends to cause a short circuit therebetween, thereby reducing the production yield.
In order to solve the above problem, a structure where the source bus lines are arranged on the first substrate while the switching elements and the gate bus lines are arranged on the second substrate (hereinbelow, such a structure is referred to as a counter source structure) is disclosed in the following literature:
(1) J. F. Clerc et al., xe2x80x9cNew Electronics Architectures for Liquid Crystal Displays Based on Thin Film Transistorsxe2x80x9d, Japan Display ""86
(2) K. Oki et al., xe2x80x9cNew Active Matrix Full Color Liquid Crystal Displayxe2x80x9d, ITEJ Technical Report, vol. 11, No. 27, pp. 73-78
(3) K. Oki et al., Japanese Laid-Open Publication No. 62-133478, xe2x80x9cActive Matrix Display Devicexe2x80x9d.
A liquid crystal display device having the counter source structure will be described with reference to FIG. 10 as the fifth prior art example.
The liquid crystal display device having the counter source structure includes source bus lines 1009 formed on a first substrate, and gate bus lines 1010, reference lines 1021 for applying a reference potential to a liquid crystal layer, pixel electrodes 1008, and switching elements 1011 formed on a second substrate. The first substrate and the second substrate are disposed facing each other with a predetermined gap therebetween. The liquid crystal layer is formed between the substrates. In the liquid crystal display device having the counter source structure, since no crossings between the gate bus lines 1010 and the source bus lines 1009 are formed on the second substrate, a short circuit between a gate bus line and a source bus line is prevented. This increases the yield in the fabrication of the liquid crystal display device. Moreover, since no crossings between the gate bus lines 1010 and the source bus lines 1009 are formed on the second substrate, the gate bus lines and the source bus liens are less affected by capacitance coupling, eliminating a problem of signal delay.
However, the following problem arises when the counter source structure shown in FIG. 10 is applied to a color liquid crystal display device.
For color display, a color filter layer composed of color layers of different colors which selectively transmit light beams having specific wavelengths must be formed on the first substrate. In the case of the counter source structure, the source bus lines are formed on the first substrate on which the color filter layer is formed. This means that no source lines made of a metal film exist at positions on the second substrate corresponding to the BM layer as in the case of the liquid crystal display device shown in FIGS. 6A and 6B. This necessitates the formation of a BM layer made of a photosensitive resin material and the like to block light from the regions other than the colored portions.
When a BM layer is provided, however, steps may be formed on the surface of the counter substrate (first substrate). In such a case, the orientation of liquid crystal molecules in the liquid crystal layer is disturbed in the vicinity of the steps, reducing the display quality. Therefore, in order to maintain good display quality, the control of the thickness of the BM layer is critical.
The liquid crystal display device of the invention includes a first substrate and a second substrate facing each other with a liquid crystal layer interposed therebetween, the first substrate including: color layers of different colors each having a plurality of colored portions; a transparent conductive film formed to cover the colored portions as a counter electrode; and a black matrix layer made of an insulating material for blocking light from regions other than the colored portions.
In one embodiment of the invention, the insulating material is a resin.
In another embodiment of the invention, the thickness of the black matrix layer is equal to or less than the thickness of the colored portions.
In still another embodiment of the invention, the first substrate includes a first common transfer electrode which is electrically connected to the counter electrode and is formed on at least one of the plurality of colored portions, and the second substrate includes a second common transfer electrode which is electrically connected to the counter electrode of the first substrate.
According to another aspect of the invention, a method for fabricating a liquid crystal display device including a first substrate and a second substrate facing each other with a liquid crystal layer interposed therebetween is provided. The method includes the steps of: a) forming a color filter having a plurality of colored portions of different colors on the first substrate; b) forming a transparent conductive film to cover the colored portions as a counter electrode; and c) forming a black matrix layer for blocking light from regions other than the colored portions by forming a black resin film on the transparent conductive film and removing portions of the black resin film located above the colored portions.
In one embodiment of the invention, the method further includes the step of scattering dielectric beads on the black matrix layer by charging the transparent conductive film with a positive or negative potential and supplying particles of the dielectrode beads charged with a potential of the same polarity as the potential at the transparent conductive film on the first substrate.
In another embodiment of the invention, the first substrate includes a first common transfer electrode which is electrically connected to the counter electrode, the second substrate includes a second common transfer electrode which is electrically connected to the counter electrode of the first substrate, and the method further includes the step of forming at least one of the plurality of colored portions on the first common transfer electrode.
Alternatively, the liquid crystal display device of this invention includes a first substrate and a second substrate facing each other with a liquid crystal layer interposed therebetween, wherein the second substrate includes: a plurality of pixel electrodes arranged in a matrix; a plurality of gate bus lines arranged in parallel with one another along near the pixel electrodes; switching elements for selectively driving the pixel electrodes; and reference lines arranged in parallel with the gate bus lines for applying a reference potential to the switching elements, wherein the first substrate includes: a color filter layer having colored portions of a plurality of colors arranged to correspond to pixel regions; and a plurality of source bus lines formed on the color filter layer to cross the gate bus lines, and wherein a black matrix layer made of a photosensitive resin material is formed to partly overlap the source bus lines and fill gaps between the colored portions, and a thickness of the black matrix layer overlapping the source bus lines is equal to or less than a thickness of the color filter layer.
In one embodiment of the invention, the thickness of the black matrix layer overlapping the source bus lines is 400 nm or more.
In another embodiment of the invention, peripheries of the colored portions are tapered, and the black matrix layer partly overlaps the tapered peripheries.
In still another embodiment of the invention, a thickness of overlap portions of the black matrix layer and the tapered peripheries of the colored portions is equal to or less than a thickness of centers of the colored portions.
Alternatively, the method for fabricating a liquid crystal display device is provided. The liquid crystal display device includes a first substrate and a second substrate facing each other with a liquid crystal layer interposed therebetween, wherein the second substrate includes: a plurality of pixel electrodes arranged in a matrix; a plurality of gate bus lines arranged in parallel with one another along near the pixel electrodes; switching elements for selectively driving the pixel electrodes; and reference lines arranged in parallel with the gate bus lines for applying a reference potential to the switching elements, wherein the first substrate includes: a color filter layer having colored portions of a plurality of colors arranged to correspond to pixel regions; and a plurality of source bus lines formed on the color filter layer to cross the gate bus lines, and wherein a black matrix layer made of a photosensitive resin material is formed to partly overlap the source bus lines and fill gaps between the colored portions, and a thickness of the black matrix layer overlapping the source bus lines is equal to or less than a thickness of the color filter layer. The method includes the steps of: forming the color filter layer having colored portions of a plurality of colors on the first substrate; forming the source bus lines made of a transparent conductive film on the color filter layer; and providing a black matrix material of a photosensitive resin on the first substrate and patterning the black matrix material by exposing a back surface of the first substrate to light with a predetermined light exposure to form the black matrix layer having a thickness equal to or less than a thickness of the color filter layer and equal to or more than 400 nm.
According to the liquid crystal display device of the present invention, the transparent conductive film is formed on the color filter layer composed of the colored portions without forming a smoothing film and the like therebetween. Accordingly, the electrode formed of the transparent conductive film has concave portions in the gaps between the colored portions corresponding to the pixel electrodes. If protrusions are formed between the colored portions, areas around such protrusions will become difficult to be rubbed desirably in a subsequent rubbing step. According to the liquid crystal display device of the present invention, such protrusions from the substrate surface are reduced at the final stage, and thus, an alignment film can be appropriately formed in the pixel portions.
Since the concave portions are originated from the surface structure of the underlying colored portions, no special concave formation step using an additional material is required. This reduces the production cost. Moreover since the black matrix layer made of a resin material (the resin BM layer) is formed filling these concave portions, the capacitance between a source bus line and the counter electrode includes a coupling capacitance via the resin BM layer as well as the liquid crystal layer. As a result, the conventional signal delay due to a capacitance at the periphery of a pixel can be suppressed. Furthermore, the slant components of the electric field from the counter electrode toward the periphery of the pixel electrode reduces, and the generation of the reverse tilt domain is suppressed. This further improves the display quality of the liquid crystal display device.
The counter electrode is continuously formed over substantially the entire top surface of the first substrate, and the insulating black matrix layer is sporadically formed thereon. Accordingly, a voltage can be easily applied to the counter electrode without damaging the counter electrode. This makes it possible to easily establish a potential difference on the surface of the first substrate, between the portions located above the colored portions and the other portions (on the BM layer). As a result, charged microparticles can be selectively placed on the BM layers.
Protrusions from the surface of the counter substrate can be reduced by forming the BM layer having a thickness equal to or less than the thickness of the color filter layer. The height of such protrusions is preferably about 500 nm, more preferably about 400 nm or less. This contributes to eliminating generation of the reverse tilt domain.
During the formation of the color filter layer, at least one colored portion is extended to a position corresponding to the second common transfer electrode formed on the second substrate. This allows for a good electrical connection (common transfer) between the first and second substrates. At this time, if a plurality of color filter layers of different colors are stacked in the common transfer portion, the cell thickness (the thickness of the liquid crystal layer) reduces in the common transfer portion. As a result, the amount of carbon paste required for the connection between the substrates reduces and the reliability against a short circuit improves.
According to the method for fabricating a liquid crystal display device of the present invention, the transparent conductive film is formed on the colored portions without forming a smoothing film and the like therebetween. Accordingly, the electrode formed of the transparent conductive film has concave portions in the gaps between the colored portions corresponding to the pixel electrodes. If portions are formed between the colored portions, areas around such protrusions will become difficult to be rubbed desirably in a subsequent rubbing step. According to the method of the present invention for forming a liquid crystal display device, protrusions from the substrate surface to be rubbed are reduced at the final stage, and thus, an alignment film can be appropriately formed in the pixel portions.
Since the concave portions originate from the surface structure of the underlying colored portions, special step and/or material are not required for forming the concave portions. This reduces the production cost.
Moreover, according to the method of the present invention, the resin BM layer is formed filling these concave portions. Accordingly, the method according to the present invention can fabricate a liquid crystal display device where the capacitance between a source bus line and the counter electrode includes a coupling capacitance via the resin BM layer as well as the liquid crystal layer. As a result, the conventional signal delay via a capacitance at the periphery of a pixel can be suppressed. Furthermore, according to the method of the present invention, the slant components of the electric field from the counter electrode toward the periphery of the pixel electrode reduces, and the generation of the reverse tilt domain is suppressed. Accordingly, a liquid crystal display device with improved display quality can be fabricated.
According to the method of the present invention, on the transparent conductive film of the first substrate charged with a positive or negative potential, particles of dielectric beads charged with a potential of the same polarity as the potential at the transparent conductive film are supplied. Such dielectric beads mostly attach to the BM layer. Accordingly, selective supply of the dielectric beads only on the BM layer is easily realized. Thus, a high-quality liquid crystal display device which can minimize scattering of transmitted light in the liquid crystal layer for each pixel electrode can be fabricated.
According to the method of the present invention, during the formation of the colored portions, at least one colored portion is extended to a position corresponding to the second common transfer electrode formed on the second substrate. Thus, according to the method of the present invention, a liquid crystal display device where a good electrical connection (common transfer) is secured between the first and second substrates can be fabricated without increasing the number of steps. In the formation of the common transfer portion, if a plurality of color layers with different colors are stacked in the common transfer portion, the cell thickness (the thickness of the liquid crystal layer) reduces in this portion. As a result, the amount of carbon paste required for the connection between the substrates reduces and the reliability against a short circuit improves.
Alternatively, the liquid crystal display device of the present invention includes the first substrate of the counter source structure and the second substrate facing each other with the liquid crystal layer therebetween. The first substrate of the counter source structure includes the color filter layer, the source bus lines, and the BM layer. The second substrate includes the pixel electrodes, the gate bus lines, the switching elements, and the reference lines. The counter source structure serves to prevent an occurrence of a defect due to a short circuit between a gate bus line and a source bus line from occurring. In the counter source structure, since no crossings between the gate bus lines and the source bus lines are formed on the same substrate, the gate bus lines and the source bus lines are less affected by capacitance coupling, eliminating a problem of signal delay.
The BM layer formed between the colored portions serves, not only to flatten the surface of the color filter substrate (first substrate) filling the concave portions between the colored portions, but also to prevent an occurrence of light leakage at regions which do no contribute to display. Since the thickness of the portions of the BM layer which overlap the source bus lines is set to be equal to or less than the thickness of the color filter layer, no steps are formed on the surface of the substrate due to protruding pattern edges of the BM layer. This prevents the orientation of liquid crystal molecules in the liquid crystal layer from being disturbed.
By setting the thickness of the BM layer at 400 nm or more, the transmittance of the BM layer made of a photosensitive resin can be reduced to 0.5% or less (see Table 2 to be presented in Example 2). Thus, an excellent contrast ratio for a liquid crystal display device can be obtained.
The BM layer may overlap the peripheries of the colored portions. In this case, if the thickness of each overlap region (the sum of the thickness of the BM layer and the thickness of the colored portion in the overlap region) is equal to or less than the thickness of the center of the colored portion, no step will be formed on the surface of the substrate due to a pattern edge of the BM layer in the overlap region, preventing the orientation of liquid crystal molecules in the liquid crystal layer from being disturbed.
For example, if the periphery of each colored portion is tapered and the BM layer overlaps the tapered periphery, no pattern edge of the BM layer will protrude from the surface of the substrate as long as the thickness of the overlap region of the BM layer and the colored portion does not exceed the thickness of the center of the colored portion.
The method for fabricating a liquid crystal display device according to the present invention includes, after the steps of forming the color filter layer having colored portions of a plurality of colors and the source bus lines made of a transparent conductive film, the steps of applying or laminating a black matrix material of a photosensitive resin to the substrate and exposing the back surface of the resultant substrate to light. During the exposure step, only portions of the BM material are exposed to light by using the color filter layer as a mask, so that the BM layer remains in the gaps between the colored portions. At this step, by adjusting the thickness of the BM material and the light exposure, the thickness of the portions of the BM layer which overlap the source bus lines can be controlled to be equal to or less than the thickness of the colored portions and equal to or more than 400 nm.
Thus, the invention described herein makes possible the advantages of (1) providing a liquid crystal display device capable of improving the display quality and reducing the production cost, and a method for fabricating such a liquid crystal display device, and (2) providing a liquid crystal display device having a counter source structure where a black matrix layer has a sufficient light blocking property, the orientation of liquid crystal molecules is not disturbed and thus providing good display quality, and the production yield is improved; and a method for fabricating such a liquid crystal display device.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.